The invention relates generally to wind turbines and more particularly to a compound planetary gear transmission unit interposed between a rotor of a wind turbine and an electrical generator.
A wind turbine 10, illustrated in FIG. 1, comprises an epicyclic gear transmission unit 12 housed within and supported by a nacelle 14 in which the gear transmission unit 12 acts to transmit torque from rotor blades 16 and rotor hub 18 to an electrical generator 20.
The use of a planetary gearbox to drive an electric generator 20 in response to rotation of a rotor 16, 18 of a wind turbine is well known. The rotor provides a low speed, high torque input to the gear transmission unit 12.
Market forces are ever demanding wind turbines with higher power outputs at a lower cost, and greater reliability. As the power output requirements increase for wind turbines, the rotational speed of the rotor blades 16 usually decreases due to noise requirements. Consequently, the input torque to the gear transmission unit 12 increases in a non-linear fashion. The foregoing limitations result in gear transmission units that are heavier and more costly. Further, the wind turbine tower 22 mass needs to increase as well to accommodate the increased top mass due to the heavier gear transmission units, further increasing the mass and cost of the overall wind turbine system.
The foregoing issues of high torque, low input RPM have generally been addressed through conventional means that may include planetary arrangements with multiple stages many times including a high-speed offset gear. Conventional compound planetary configurations using three planets have also been employed; while one approach includes seven planets with flexible pins and a dual planetary system in which the input shaft drives the first stage planets as well as the ring gear of the second stage. The sun of the second stage, which includes five planets and flexible pins, drives the ring gear of the first stage. The sun of the first stage is directly connected to a large third stage gear that drives the output high-speed gear.
In view of the foregoing, it would be both advantageous and beneficial to provide a gear transmission unit having a torque density that is sufficient to substantially reduce the nacelle weight and the tower weight for a wind turbine beyond that achievable with existing wind turbine gear transmission units.